Today, there are hundreds of millions of people in the United States and around the world who wear eyeglasses or contact lenses to correct ocular refractive errors. The most common ocular refractive errors include myopia (nearsightedness), hyperopia (farsightedness), astigmatism, and presbyopia. Each of these ocular refractive errors can be modified, reduced, or corrected by reshaping the cornea of a patient's eye.
Various procedures have been used to correct ocular refractive errors. For example, laser thermal keratoplasty (LTK) uses laser light to heat the cornea, which causes shape changes in the cornea. Other surgical eye procedures may use radio frequency signals or other techniques to heat the corneal tissue in a patient's eye.
It has long been believed that these types of surgical eye procedures modified the shape of the cornea due to shrinkage of stromal collagen in the eye. In other words, these procedures were based on the idea that heating the cornea produces thermal shrinkage of stromal collagen in the cornea, leading to structural modifications of the cornea (including anterior surface shape changes that modify, reduce, or correct ocular refractive errors). This belief was reinforced by experimental results of Stringer and Parr (1964), which found that corneal stromal collagen may shrink when heated to a temperature of at least 56.9° C.±1.9° C. for a lengthy period of time. Other experiments, such as those involving scanning electron microscopy to image LTK-induced corneal shape changes, supported this belief.